1. Field of the Invention
The present inventions relate to watercraft control, more particularly to a controller for a propulsion unit, a control program for a propulsion unit controller, a method of controlling a propulsion unit controller, and a controller for watercraft operation, which can be used for controlling a plural number of propulsion units of a watercraft.
2. Description of the Related Art
Methods of facilitating boat handling have been conventionally proposed to direct a boat in any intended direction while holding the bow direction or bow turning speed constant. Such an operation can be accomplished by utilizing geometric relationships among positions of the instantaneous boat center and plural propulsion units, and resultant vector of propulsion forces. These methods provide the effect of facilitating approach to or departure from a pier, which can be difficult, for example, in rough water.
In most of the proposed methods, at least one propulsion unit is mounted on the stern of the watercraft. A plurality of small propulsion units, commonly known as “side thrusters” are mounted on the bow or other locations on the boat. Using the geometric relationships as described, propulsion forces are appropriately adjusted to run the boat in any intended direction while holding constant the bow direction or bow turning speed.
Application of such proposed methods to a small boat results in many disadvantages such as increase in cost due to the additional hardware including the side thrusters, changes in shape for securing mounting positions, and deterioration in fuel economy due to increase in hydrodynamic resistance generated by the side thrusters.
Other proposed methods include using a boat is with two propulsion units, one each at port stern and starboard stern. In these methods, the boat can be moved in any intended direction by controlling propulsion forces appropriately while keeping the bow direction or bow turning speed constant. This method utilizes the geometric relationships among positions of the instantaneous boat center and the plural propulsion units, as well as the resultant vector of propulsion forces to obtain the same effects without the disadvantages associated with the above method using the side thrusters.
For example, the Japanese Patent Application Publication JP-B-2810087 discloses an invention related to a mechanism for appropriately handling the resultant vector of propulsion forces produced with port and starboard propulsion units.
Other methods for controlling a watercraft position have also been proposed. For example, because anchoring is not possible in deep water, such as in the open ocean, boaters who wish to maintain a fixed position typically periodically re-start and drive the boat to compensate for drift. Alternatively, when fishing, the engine can be left running but disengaged, i.e., in neutral, so that the boat is allowed to drift slowly from a starting point. When the boat drifts a certain distance from the start point, the engine is engaged to return the boat back to the start point, and again disengaged to drift. This operation is repeated.
In a form of troll fishing, the boat is required to drift slowly with the bow preferably directed toward the wind. Leisure fishing boats having only one shaft IB can be held in such a position by relying on the main keel of the hull and a spanker (sail) on the stern. Such an arrangement is disclosed in Japanese Examined Patent Application Publication JP-A-2003-26095.